Biochemical mechanisms of rhizospheric Bacillus subtilis-facilitated phytoextraction by alfalfa under cadmium stress – Microbial diversity and metabolomics analyses

• Published in: Ecotoxicology and environmental safety 2021-04, Vol.212, p.112016, Article 112016
• Main Authors: Li, Qi, Xing, Yingna, Fu, Xiaowen, Ji, Lei, Li, Tianyuan, Wang, Jianing, Chen, Guanhong, Qi, Zhichong, Zhang, Qiang
• Format: Article
• Language: English
• Subjects: Bacillus subtilis - growth & development; Bacillus subtilis - metabolism; Bacteria; Biodegradation, Environmental; Biodiversity; Biomass; Cadmium - analysis; Cadmium - metabolism; Heavy metal mobilization; Medicago sativa - metabolism; Medicago sativa - microbiology; Medicago sativa L; Metabolite; Metabolomics; Phytoremediation; Rhizosphere; Soil - chemistry; Soil Microbiology; Soil Pollutants - analysis; Soil Pollutants - metabolism
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2021.112016

The effects of Bacillus subtilis inoculation on the growth and Cd uptake of alfalfa were evaluated in this research using pot experiments, and the relevant biochemical mechanisms were first investigated by combined microbial diversity and nontarget metabolomics analyses. The results indicated that inoculation with alfalfa significantly decreased the amount of plant malondialdehyde (MDA) and improved the activities of plant antioxidant enzymes and soil nutrient cycling-involved enzymes, thereby promoting biomass by 29.4%. Inoculation also increased Cd bioavailability in rhizosphere soil by 12.0% and Cd removal efficiency by 139.3%. The biochemical mechanisms included enhanced bacterial diversity, transformed microbial community composition, regulated amounts of amino acids, fatty acids, carbohydrates, flavonoids and phenols in rhizosphere soil metabolites, and modulations of the corresponding Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. These responses were beneficial to microbial activity, nutrient cycling, and Cd mobilization, detoxification, and decontamination by alfalfa in soil. This study, especially the newly identified differential metabolites and metabolic pathways, provides new insights into mechanism revelation and strategy development in microbe-assisted phytomanagement of heavy metal-contaminated soils. [Display omitted] •Bacillus subtilis inoculation markedly promoted the growth and Cd uptake of alfalfa.•The rhizobacteria enhanced microbial community diversity and enzyme activity in soil.•Metabolomics mechanisms for bacteria-aided phytoextraction were firstly demonstrated.•Regulated metabolites included amino acids, fatty acids, carbohydrates and flavonoids.•Inoculation improved Cd mobilization, detoxification and decontamination by alfalfa.